i tried all the things suggested here and nothing worked. addwitnessaddress command doesnt exist in bitcoin-qt, the electrum script in the other thread just returns p2pkh: prefix to the same private key, and bitcoin-qt does not recognize either p2wpkh: or p2pkh:
maybe it just wont work until a future version of bitcoin-qt
As per post as suggested that it needs a good PC for this to work out. Maybe your PC does not compatible in creating a btc vanity address or try checking the steps again and double check if it has being done correctly. There are times that process might not be followed like forgetting a tiny details in the process.